(a) Irrigation areas in the Nile Valley
(i) Lower Nile valley from the Aswan Dam to the Delta in Egypt.
(ii) Sennar (Sudan).
(iii) Kenena (Sudan).
(iv) Middle Nile valley in the Sudan.
(v) Kasm-el-Girba area along the Atbara in Eastern Sudan.
(vi) Khasimel Girba (Egypt).
(vii) Lake shores.
(b) Description of the Perennial method of irrigation
(1) Mostly, modern methods of irrigation are used in the Nile valley.
(2) Dams and barrages are built across the Nile
(3) Dams hold back some of the Nile water during the floods.
(4) Water stored behind the dams is released especially when the level of the rivers is low.
(5) Water is allowed to flow by gravity to the cultivated land below the dam.
(6) By releasing the water, farming takes place throughout the year.
(7) The most important of these dams is the Aswan Dam.
(8) Some other dams in this areas are Jebel Aulia, Sennar, etc.
(c) Problems created by irrigation in the Nile valley.
(i) Irrigation uses up the water which otherwise could have been used for other demands, e.g. Hydro electric power generation, transportation, etc.
(ii) The creation of the Nasser lake by the Aswan Dam led to the submergence of several settlements and displacement of over 50,000 persons who had to be resettled in the Kasm-el-Girba area in the Sudan.
(iii) The holding back of some silt and other sediments by the lakes and dams has prevented them from reaching the lower Nile valley in Egypt and were deposited there.
(iv) The reduction in the sediments load of the lower Nile has decreased the rate at which sand banks are being built in the delta. The result of this is that the Mediterranean Sea has flooded over 400,000 hectares of fertile farmlands.
(iv) Fluctuation in the volume of water and salination.
(v) Social problems of displaced people (resettlement) and collapsed dam.
(vi) Retained water in the dams creates diseases e.g. Bilharzia, river blindness.
(vii) Growth of water weeds.
(viii) Decrease in amount of fresh water has led to decline of fishing industry in Egypt.